1. Field of the Invention
The present invention relates to a method of forming a resist pattern using a chemically amplified resist composition, and relates specifically to a method of forming a resist pattern that utilizes a double patterning process in which a first patterning is performed using a first chemically amplified resist composition, and a second chemically amplified resist composition is then applied and subjected to a second patterning.
2. Description of the Related Art
Techniques (pattern-forming techniques) in which a fine pattern is formed on top of a substrate and a lower layer beneath that pattern is then processed by conducting etching with this pattern as a mask are widely used in the semiconductor industry for IC fabrication and the like, and are attracting considerable attention.
These fine patterns are typically formed from an organic material, and are formed, for example, using a lithography method or a nanoimprint method or the like. For example, in a lithography method, a resist film composed of a resist material that exhibits changed solubility in a developing solution upon exposure is formed on a support such as a substrate, and the resist film is subjected to selective exposure of radial rays such as light or an electron beam, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film. Then, using this resist pattern as a mask, a semiconductor element or the like is produced by conducting a step in which the substrate is processed by etching.
A resist material in which the exposed portions develop increased solubility in the developing solution is called a positive-type, and a resist material in which the exposed portions exhibit reduced solubility in the developing solution is called a negative-type.
In recent years, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization. Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are now starting to be introduced in mass production, and pattern formation at 45 nm level resolution is now possible with lithography using an ArF excimer laser. Moreover, in order to achieve further improvements in resolution, research is also being conducted into lithography techniques that use exposure light source having a wavelength shorter than these excimer lasers, such as F2 excimer lasers, electron beams, extreme ultraviolet radiation (EUV), and X rays.
Resist materials require lithography properties that include a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources. A chemically amplified resist composition that includes an acid generator that generates acid upon exposure can be used as a resist material that satisfies these conditions. In addition to the above acid generator, a chemically amplified resist composition usually includes a base component that exhibits changed solubility in an alkali developing solution under the action of the acid generated from the acid generator, and for example, the base component in a positive chemically amplified resist uses a component that exhibits increased solubility in an alkali developing solution under the action of acid (for example, see Patent Document 1). Further, a resin is normally used as the base component of a chemically amplified resist composition.
As a technique for further improving the resolution, a lithography method called liquid immersion lithography (hereafter, frequently referred to as “immersion exposure”) is known in which exposure (immersion exposure) is conducted in a state where the region between the objective lens of the exposure apparatus and the sample is filled with a liquid (an immersion medium) that has a larger refractive index than the refractive index of air (for example, see Non-Patent Document 1).
With this type of immersion exposure, it is considered that higher resolutions equivalent to those obtained using a shorter wavelength light source or a higher NA lens can be achieved using the same exposure light source wavelength, with no reduction in the depth of focus. Furthermore, immersion exposure can be conducted using existing exposure apparatus. As a result, it is expected that immersion exposure will enable the formation of resist patterns of higher resolution and superior depth of focus at lower costs. Accordingly, in the production of semiconductor elements, which requires enormous capital investment, immersion exposure is attracting considerable attention as a method that offers significant potential to the semiconductor industry, both in terms of cost and in terms of lithography properties such as resolution.
Immersion lithography is effective in forming patterns having various shapes. Further, immersion exposure is capable of being used in combination with currently studied super-resolution techniques, such as phase shift methods and modified illumination methods. Currently, techniques using an ArF excimer laser as the exposure source are the most actively studied immersion exposure techniques. Further, water is mainly being investigated as the immersion medium.
Recently, a new lithography technique called a double patterning process has been proposed, in which a resist pattern is formed by conducting patterning two or more times (for example, see Non-Patent Documents 2 and 3).
There are a number of varieties of double patterning processes, and examples include (1) a method in which a lithography step (from application of a resist composition through to exposure and developing) and an etching step are performed two or more times to form a pattern, and (2) a method in which the lithography step is repeated twice or more in succession.
Pattern formation using method (1) is executed, for example, using the sequence described below. First, a laminate is prepared by laminating a substrate, an underlayer film and a hard mask. Next, a resist film is provided on top of the hard mask, and the resist film is selectively exposed through a photomask and developed, thus forming a first resist pattern in which a plurality of resist patterns of predetermined size are positioned at predetermined locations. Subsequently, the hard mask is etched using the first resist pattern as a mask, and the remaining first resist pattern is then removed. This yields a hard mask to which the first resist pattern has been transferred. Next, a resist composition is applied to the hard mask, forming a resist film that fills the gaps within the hard mask. This resist film is then selectively exposed through a photomask having different pattern positioning and developed, thus forming a second resist pattern. Subsequently, the hard mask is etched using the second resist pattern as a mask, and the remaining second resist pattern is then removed. This yields a hard mask to which both the first resist pattern and the second resist pattern have been transferred. By subsequently conducting etching using this hard mask as a mask, the pattern in the hard mask can be transferred to the underlayer film, and as a result, a pattern is formed having a narrower pitch than the photomask that was used.
In the method (2), for example, a first resist film is formed on top of a support, a plurality of resist patterns are formed by patterning the resist film, a second resist material is then applied, thereby forming a second resist film that fills the gaps within the above plurality of resist patterns, and the second resist film is then subjected to patterning.
By using these double patterning processes, a resist pattern can be formed that has a higher resolution than a resist pattern formed using only a single lithography step (single patterning), even when a light source having the same exposure wavelength is used, and even when the same resist composition is used. Further, a double patterning process can be performed using an existing exposure apparatus.
[Patent Document 1]
Japanese Unexamined Patent Application, First Publication No. 2003-241385
[Non-Patent Document 1]
Proceedings of SPIE, vol. 5754, pp. 119 to 128 (2005)
[Non-Patent Document 2]
Proceedings of SPIE, vol. 5256, pp. 985 to 994 (2003)
[Non-Patent Document 3]
Proceedings of SPIE, vol. 6153, pp. 615301-1 to 19 (2006)
In those cases where a chemically amplified resist composition is used to form an isolated space pattern (trench pattern) or a hole pattern, and particularly in the case where a positive composition is used, the pattern formation is constrained to formation using a weaker incident light intensity than that used when an isolated line pattern, a line and space pattern or a dot pattern is formed, and therefore the contrast between the light intensities irradiated onto the exposed portions and the unexposed portions is small. As a result, restrictions tend to exist on the pattern formability during the resist pattern formation, including the resolution and the lithography margins (for example, the allowable margins for the exposure dose and the depth of focus (the EL margin and DOF margin respectively), and the degree of verticalness of the pattern shape), meaning it tends to be very difficult to form a resist pattern having high resolution.
One possible technique for forming a high-resolution resist pattern involves using the type of double patterning process described above. However, of the double patterning processes described above, the method (1) requires that resist film patterning is performed at least twice and etching of the underlying hard mask is performed at least twice in order to form a pattern on the substrate, which is problematic in terms of the increased number of steps, the increased amounts of reagents that must be used, and the associated increase in production costs. Further, the method (2) is suited to formation of a line and space pattern, but is unsuited to the formation of an isolated space pattern (trench pattern) or a hole pattern.
Accordingly, a novel technique that enables an isolated space pattern or a hole pattern to be formed at a high resolution has been keenly sought.